The disclosure of Japanese Priority Application No. 2000-362058 filed Nov. 29, 2000, is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a position detecting device and method of a lens barrel that adjusts lens focusing and changes a focal length of an optical system by moving a focusing lens group back and forth along an optical axis.
2. Description of Related Art
It is known to provide a lens barrel that adjusts lens focusing and changes a focal length by moving a focusing lens group back and forth along an optical axis. One known type of such device detects a position of a member, such as a cam barrel, by using a position detecting device. The detected member is driven in the lens barrel upon auto focusing or changing of a focal length, and then the lens obtains information on a focusing distance and a focal length, thereby controlling camera exposure or flash amount.
For example, in order to obtain a focusing distance in the conventional lens, a distance measuring encoder is used. One method of arranging the distance measuring encoder within the lens is to place it between a fixed barrel and a member for rotating a worm gear or a cam mechanism for driving a focusing lens, in which the member rotates about the optical axis without moving along the optical axis. The rotational position of the member is measured to know the lens position. Another method for arranging the distance measuring encoder within the lens is to place it so as to detect direct movement of a focusing lens in a direction along the optical axis.
In the former method, the member rotating about the optical axis is provided at the last stage of a gear mechanism of a lens driving mechanism, and rotates the worm gear or the cam for driving the focusing lens. The distance measuring encoder for detecting distance information is placed between the rotating member of the last stage and the fixed barrel. In this case, a brush for detecting distance information is attached to the rotating member, and a flexible printed circuit board having an encoder pattern for indicating a position is attached to the fixed barrel. Thus, the brush detects distance information based upon its position.
In the latter method, in order to detect direct movement of a focusing lens in a direction of the optical axis by using the distance detecting encoder, the brush for detecting distance information and the flexible printed circuit board having an encoder pattern are provided near the focusing lens.
However, in the former case, for example, as the rotating member of the last stage of the gear mechanism rotates about the optical axis and rotates the worm gear or the cam mechanism for driving the focusing lens, it is necessary to have some space in which the last-stage rotating member is supported and rotated through an angle of 360xc2x0 inside the fixed member. Then, in a type of zoom lens in which a focusing lens group is arranged on the subject side and a rear lens group is moved toward the front of the zoom lens by zooming, a lens frame of the rear lens group must be arranged inside the rotating member that is rotated about the optical axis. This type of arrangement requires a certain amount of space, which makes it difficult to reduce the size of the lens.
In the latter case, in order to detect direct movement of the focusing lens in a direction of the optical axis by using the distance measuring encoder, the brush for detecting a distance and the flexible printed circuit board having the encoder pattern are placed near the focusing lens. A lens in which a focusing lens group is moved by zooming is often used in this case. In this type of zoom lens, when the brush for detecting a distance and the flexible printed circuit board having the encoder pattern are placed near a focusing lens, the flexible printed circuit board is attached to a member that is moved while zooming is performed. Since the flexible printed circuit board needs to be long enough to move with this member during zooming, the flexible printed circuit board is accommodated into the lens barrel in a manner such that the flexible printed circuit board is folded in the shape of an xe2x80x9cSxe2x80x9d. However, this manner of accommodation causes a problem in that a large space is needed to contain the flexible printed circuit board in the lens barrel. In addition, since the flexible printed circuit board is bent each time a zooming operation is performed, the flexible printed circuit board can become damaged and degraded over time.
It is one object of the invention to provide a position detecting device and method of a lens barrel that has a smaller size, high space-usage efficiency, high durability and high reliability.
According to one aspect of the invention, which is applicable to a lens barrel including an optical system, an optical system driving member that moves at least part of the optical system, and a driving force transmitting member that transmits rotational driving force from a driving source to the optical system driving member, a position detecting device is provided that includes a linear moving member that converts rotational motion of the driving force transmitting member into a linear motion, and a detecting unit (detector) that detects the linear movement of the linear moving member. This aspect of the invention is capable of addressing the problems discussed above, for example.
According to another aspect of the invention, the driving force transmitting member is a rotating shaft-like member that rotates through at least one rotation.
According to another aspect of the invention, the position detecting device includes a backlash eliminating member that eliminates a backlash between the driving force transmitting member and the linear moving member by moving toward one direction. According to a preferred embodiment, the backlash eliminating member includes a spring.